In an automation system measurement data, control signals for actuators, etc. may be handled by several modules designed for such purposes. Modules are often coupled to the automation system via a bus which may transfer signals between the modules and other parts of the automation systems. The bus may also be called as an I/O bus (input/output). Because several modules are coupled to the same bus there is a need to provide some kind of addressing method so that messages can be delivered to correct recipients via the I/O bus. An addressing solution is to provide so called DIP switches or corresponding switchable elements in the modules wherein each module may be set with an individual address by setting the switches accordingly. However, each address bit of the address needs one switch and also one address line in the I/O bus. Hence, to be able to distinguish (address) e.g. 16 different modules one needs to have four address lines in the bus and four switches in each module. The switches occupy some space from the modules and may prevent size reduction of the modules. Moreover, a user may erroneously turn the DIP switches into incorrect positions, wherein the address indicated by the DIP switches is not correct.